Effects of Oil Contamination on Range of Soil Types in Middle Taiga of Western Siberia

Abstract

This study examines the effects of oil contamination on three soil types—podzolic, sod-gley, and alluvial—in Western Siberia’s middle taiga, assessing key physical and chemical properties and the influence of the surfactant Modified Syntherol (MS) on oil degradation. In controlled laboratory experiments, oil was introduced at 50, 100, and 150 g/kg concentrations. Results indicate a substantial increase in soil pH, most notably in podzolic soils, alongside a significant decline in cation exchange capacity (CEC). For example, CEC in podzolic soils dropped five-fold at higher contamination levels, reflecting a reduced ability to retain essential nutrients. The water retention capacity decreased in all soil types, with the most pronounced decline observed in alluvial soils’ capillary moisture levels. MS application did not accelerate oil degradation; even after 35 days, natural decomposition rates in untreated soils remained low (0.02–0.4%), underscoring the persistence of oil contaminants. Notably, podzolic soils showed the highest susceptibility to oil contamination due to their acidic and low-organic nature, in contrast to sod-gley and alluvial soils, which demonstrated moderate resilience. These findings highlight the need for soil-specific remediation approaches, as general methods may be ineffective for soils with differing vulnerabilities and recovery capacities. This research provides essential insights for developing effective, tailored strategies to address the environmental challenges of oil pollution, advancing sustainable soil management practices for sensitive taiga ecosystems.

1. Introduction

Oil pollution represents a significant and persistent global environmental challenge, with a widespread and destructive impact on ecosystems. The contamination of soil by oil, even at relatively low levels, has a significant impact on the chemical, physical, biological and morphological properties of the soil. These changes disrupt the soil structure, hinder the activity of soil organisms and compromise plant health, ultimately affecting the broader ecosystem [1]. The study of oil pollution impacts on natural environments is therefore a topic of interest to scientists across disciplines, highlighting the need for a multifaceted approach to understanding and mitigating these effects [2,3,4,5,6].

Russia has conducted extensive research on oil pollution, particularly in Western Siberia and the northern regions, where major oil fields are located [7,8,9]. However, oil pollution issues are similarly prevalent in other parts of the world, including Saudi Arabia, Nigeria and the United States [2,7]. Each of these countries faces unique challenges due to their environmental and industrial conditions. In the Russian Federation, the oil contamination issue is particularly prevalent in the Khanty-Mansi Autonomous Okrug-Yugra and the Komi Republic, affecting podzolic and taiga soils. These regions are affected by both crude oil spills and operational pollution from oil extraction and transport activities. This has resulted in soil acidification, decreased nutrient availability and hydrophobic soil conditions. The challenging climatic conditions in these regions present an additional obstacle to soil remediation efforts [7]. Low temperatures impede natural biodegradation processes, reducing the efficacy of microbial treatments [4,8]. Similar issues are evident in the Niger Delta region of Nigeria, where extensive oil extraction activities have caused widespread contamination [9]. The tropical soils of this region, which are often rich in organic material, are highly susceptible to hydrocarbon contamination. Oil spills and leaks from pipelines and refineries have resulted in soil infertility, increased erosion, and a decline in biodiversity, particularly in sensitive mangrove ecosystems. The persistence of oil in these soils has a detrimental impact on both plant life and the livelihoods of communities that rely on the land and aquatic resources [10,11]. The warmer climate of the Niger Delta allows for greater microbial activity than that which is typical in Russia’s colder regions. However, the scale and frequency of spills in this area overwhelms the natural remediation capacity, resulting in severe and long-lasting soil degradation [9]. In Saudi Arabia, the extensive desert landscapes and arid soils are also susceptible to oil pollution, particularly in areas with major oil production facilities [12]. Despite the significant differences between the sandy soils of arid regions and the organic-rich soils of Nigeria, oil contamination still results in water repellency, a reduction in soil porosity and increased soil compaction. These changes impair the soil’s ability to retain moisture, which is already scarce in desert environments, thus exacerbating water scarcity issues [13]. Furthermore, the high temperatures in Saudi Arabia result in the rapid evaporation of volatile oil components, leaving behind heavier residues that bind tightly to soil particles, thereby increasing the difficulty of remediation efforts [14]. The United States has also faced significant environmental challenges as a result of oil contamination, most notably in the wake of the 2010 Deepwater Horizon oil spill in the Gulf of Mexico. The oil spill had a significant impact on coastal soils and marshes along the Gulf Coast, with the oil penetrating deep into the soil layers and disrupting the structure and function of these coastal ecosystems [15]. It has been demonstrated that contamination of these sandy and loamy soils has resulted in a reduction in microbial diversity, decreased water infiltration and impeded plant regeneration in marsh areas [16]. Furthermore, the toxic effects of hydrocarbons posed long-term threats to the resilience of these ecosystems, necessitating comprehensive remediation strategies that integrated bioremediation with physical removal techniques [17].

It is essential to understand the physical properties of soils, such as water retention, porosity and compaction, in order to grasp soil fertility and resilience. These properties directly affect processes that are crucial for mechanical cultivation, agronomic practices and the habitat conditions of soil organisms [18,19]. However, these properties are often examined only as supplementary characteristics in studies focused primarily on chemical and biological indicators. It is crucial to gain insight into how oil pollution impacts these physical properties, particularly in soils with diverse textural compositions. The effects may vary significantly based on the soil’s physical makeup, making this an essential area of research.

A variety of techniques are used to address the negative impacts of oil contamination [4,7,14,16,18,20]. The success of these methods hinges on a comprehensive grasp of soil characteristics, including pH levels, water retention and cation exchange capacity. These properties can undergo significant alterations due to oil contamination, underscoring the importance of a thorough understanding in the remediation process. It is therefore essential to have a comprehensive understanding of these soil properties in order to ensure effective remediation and to achieve the desired outcomes of restoration efforts [18].

Concurrently, research was conducted to develop methodologies and technologies for the reclamation of disturbed lands. Biological treatment typically involves the conversion of pollutants into non-toxic forms through microbiological processes, with the potential for the complete mineralization of hydrocarbons to carbon dioxide and water. Several bioremediation technologies for petroleum-contaminated soils propose the introduction of microorganisms that are specialized for the decomposition of existing hydrocarbons [21]. However, in some cases, the introduced microorganisms are unable to compete with the soil microbiota. Furthermore, the concentrations of the substrate in the environment may be insufficient to support the growth of the introduced strains, or the introduced microorganisms may ignore the target contaminant if alternative substrates are present [22]. In some instances, the introduction of microorganisms for the purpose of cleaning up soil contaminated with petroleum hydrocarbons has been observed to result in an increase in the cost of bioremediation with no discernible benefit [23,24]. Consequently, bioremediation technologies based on the stimulation of the indigenous microbiota of contaminated soil capable of decomposing pollutants are being actively developed. The creation of optimal conditions for microbial decomposition of hydrocarbons is a prerequisite for the success of these remediation technologies. These conditions include the provision of aerobic conditions, available nutrients, a certain soil moisture, pH, temperature, and other factors [21]. Additionally, the implementation of microbial bioremediation measures is essential. One such remediation measure is the treatment of oil-contaminated soil substrates with surfactants [25]. Moreover, surfactants have been identified as the most prevalent chemical reagent employed in the oil industry. They are employed to enhance the efficacy of oil production, for instance, to facilitate the removal of hydrocarbons from the bottomhole zone, as well as to improve filtration rates and the quality of oil reservoir openings. The use of surfactants to reduce surface tension at phase boundaries serves to diminish hydraulic resistance when transporting high-viscosity oils and oil emulsions. Surfactants are employed to enhance the dewatering process of heavy, high-viscosity oil, both during in-line demulsification and at the final stage of treatment. Additionally, they are utilized to disrupt emulsions of heavy, high-viscosity oil [26]. Furthermore, surfactants are instrumental in the prevention of corrosion of downhole equipment. The adsorption layer formed by the surfactant protects the metal surface from contact with corrosive liquids and gases [27,28]. It can be observed that the composition of pollutants in oil-contaminated soils frequently includes surfactants in conjunction with petroleum hydrocarbons. The presence of these pollutants can affect the processes of self-purification and self-restoration of soil ecosystems that have been polluted by oil and oil products in some way. These intricate biogeochemical processes of contaminant transformation are linked to the gradual restoration of oil-contaminated soil biocenoses. The duration of the individual stages of these processes varies across different natural zones, largely due to variations in soil and climatic conditions [8].

It is also noteworthy that in recent years, Russian oil companies have initiated the development of new oil fields in remote areas of the Khanty-Mansi Autonomous Okrug-Yugra region, such as the Evra River basin in the Yugra region. These areas were previously considered to be of limited ecological significance and to have minimal potential for disturbance. There is a concern among scientists that the development of new oil fields may lead to significant environmental challenges in the future [7]. It is therefore of great importance to analyze the accumulation and elimination of petroleum hydrocarbons in the main soil types of the Evra River basin, both with and without the presence of surfactants used in oil production. The results obtained will facilitate a deeper understanding of the processes occurring in the soils of the middle taiga of Western Siberia under oil pollution, enable an assessment of their ability to self-repair, and facilitate the selection of the most appropriate remediation methods.

The objective of the present study was to examine the physical and chemical characteristics of soil in new oil fields in remote areas of Western Siberia and to assess its capacity for self-repair following contamination with crude oil in a laboratory setting, with and without the addition of an industrial-used surfactant. By conducting a controlled analysis of how soil types in new oil fields in remote areas of Western Siberia react to oil contamination, this research provides valuable insights into the differential impacts on soil properties and offers guidance on how to address the long-term environmental challenges in sensitive taiga ecosystems of Western Siberia.

2. Materials and Methods

2.1. Soil Collection and Characterization

The soils of the middle taiga subzone in the Kondinsky district, Khanty-Mansiysk Autonomous Okrug-Yugra, within the Evra River basin (59°96′84.93″ N, 64°28′28.58″ E) was the object of research. Soil excavations including transects, and natural and artificial outcrops opened by rivers and roads were used for the description of soils and underlying rocks. A total of 38 transects were located in different geological and geomorphological sections. In describing the transects, its number, date, location and georeferencing were specified, and the general relief, as well as meso-, micro- and nano-relief, position of the transect in relation to the relief, vegetation, soil-forming rock, groundwater table or permafrost depth were carefully characterized. The samples were taken layer by layer, with one sample from each genetic zone horizon (between 0 and 15 cm). The soils were rationalized, air-dried at room temperature, ground in a mortar, sieved through a sieve with holes of 1 mm and thoroughly mixed.

pH of the water extract, pH of the salt extract, cation exchange capacity and hydrosorption properties were determined according to previously described methods [29,30,31]. For measuring the pH_H2O, a 1:5 soil/water suspension was prepared and mechanically shaken for 1 h, then a glass electrode was introduced for measuring pH of soil suspension. The pH_KCl of the soil solution was determined by a glass electrode with a 1:2.5 (volume fraction) suspension of soil in 1 mol/L potassium chloride solution (pH in KCl). The cation exchange capacity was assessed by extracting exchangeable hydrogen and aluminum ions from the soil using a 1 mol/L KCl solution at a soil-to-solution ratio of 1:2.5, followed by potentiometric titration of the filtrate with sodium hydroxide until reaching a pH of 8.2. The weight method was used to determine soil moisture content by drying a moist soil sample to a constant weight. This was achieved by first weighing the fresh sample and then drying it in an oven at a consistent temperature until no further weight loss was observed. The moisture content was then calculated as a percentage of the weight lost during drying relative to the oven-dried soil weight, as per the formula: Soil Moisture Percentage (%) = [(Wet Soil Weight − Dry Soil Weight)/Dry Soil Weight] × 100 [32]. (See Figure 1).

2.2. Surfactant and Petroleum Investigations

Light oil with the density of 0.818 g/cm³ from Fedorovskoye oil field, Khanty-Mansi Autonomous Okrug-Yugra region, Russia, was selected as a model source of oil pollution. The soil samples were contaminated with oil in three concentrations: 50, 100, and 150 g/kg, respectively. The oil concentration levels ranging from 50 g/kg to 150 g/kg were chosen because a concentration of 50 g/kg can be considered moderate contamination compared to the regional standard of 20 mg/kg [33]. The higher concentrations are considered high oil contamination. Concentrations above 150 g/kg were not included in the study, as the results indicated that soils experienced significant changes at the initial 50 g/kg concentration, and further increases did not notably exacerbate these effects, suggesting a threshold for soil response to oil contamination in this experimental context. Uniformity of oil distribution in soil at its model contamination was provided by continuous stirring of soil with added polluting oil in a sealed vessel in a ball mill activator at a speed of 1 revolution per second during a day. Then, the sample preparation was carried out in accordance with the requirements for the determination of mass concentrations of oil products in soil samples by the gravimetric method (PND F 16.1.41-04) [34].

To study the effect of surfactants on the physicochemical properties of the soils, the non-ionic surfactant “Modified Syntherol” (MS) (SpetsNefteGazProduct-Agidel, Sterlitamak, Russia) was used as a model surfactant; this reagent is employed by oil companies to maintain the reservoir pressure and to work in the bottomhole zone in wells. MS represents a modification of non-ionogenic surfactant Syntherol (R-C₆H₄-O(C₂H₄O)_nCH₂COONA, where R is isononyl; n—10 or 12) in a calcium chloride salt solution. The surfactant was applied to the soil samples at a concentration of 1% in soil/surfactant ratios of 1:2 and 1:4. The samples were then allowed to air-dry, to be analyzed according to PND F 16.1.41-04 [34]. In short, a soil sample weighing 30–40 g was moistened with chemically pure chloroform (CHCl₃) in a glass container, covered with 15 mL of chloroform, and agitated for 5 min on a shaker platform at room temperature. The resulting liquid was filtered through a paper filter (white tape, pore size 5–8 μm). This process was repeated 3–4 times to obtain a colorless extract. The extract was then transferred to a flask with a pointed bottom and evaporated using a rotary evaporator. The quantity of oil products (TPH) present was determined by the weight of the dry residue and expressed in mg/kg of the initial dry mass of the soil sample.

2.3. Data Processing

The statistical data were processed by the software Statistica (13.3.721) and MSExcel (16.0.14332.20763). A single-factor ANOVA was conducted to evaluate the discrepancy in the alteration of valuable soil characteristics between groups of soil samples in the absence and presence of oil contamination. All the measurements were repeated 3 times. The results were considered statistically significant at p < 0.05.

3. Results

In terms of structure, composition, and properties, 38 selected soil samples can be divided into 9 subtypes, which, based on their classification position, can be grouped into 4 main categories: podzolic type (podzolic, gley-podzolic, sod-podzolic), sod-gley type (sod-soil-gleyey, sod-surface-gleyey, humus-soil-gleyey), bog type (bog-top-peat), and alluvial type (peat, sod). The soil classification process involved an assessment of the content of different forms of iron in the selected soils. This was performed to identify elementary soil-forming processes, which would then be used to classify soils in a more precise manner. This approach is based on the substantive-genetic approach, which forms the basis of the ‘Classification and Diagnostics of Soils of Russia’ [35].

3.1. Effects of Oil on Physical–Chemestry Characteristics of Soil Samples

In order to ascertain the impact of oil on soil properties, a series of experiments was conducted, involving the examination of three distinct soil types: podzolic, sod-gley, and alluvial. Due to the peculiarities of the structure of the bogs and the lack of methods for determining the main indicators, model experiments were not performed on the bogs.

Initially, the change in the pH of the water and salt extracts of the control sample and the presence of oil products at a concentration of 50 to 150 g/kg was determined (Figure 2). Figure 2 illustrates that the introduction of oils to the soil sample at a concentration of 50 g/kg results in a rise in the pH of the salt and water extracts from the soil in a range of 0.4–0.66 pH units. For example, in the control sample, the pH values for the salt and water extracts from the soils were 3.6 and 5.8 (p < 0.005), respectively (of the podzolic type). In contrast, in the presence of oil products (50 g/kg), these values increased to 4.3 and 6.5 (p < 0.005), respectively (for the same type of soil). Furthermore, the increase in the pH values observed in the presence of oil products was also observed in other soil types, demonstrating the generality of this phenomenon. It is noteworthy that the elevated concentrations of the oil products (100 and 150 g/kg) did not result in a greater alteration of the pH values of the water and salt extracts from the soil samples. It can be postulated that an addition of oil products in a concentration of 50 g/kg will likely lead to a significant degradation of the soil system. Consequently, the concentrations of oil products in the range of 100 and 150 g/kg are unlikely to have a further detrimental impact on the soil samples.

In the presence of oil products, the cation exchange capacity and absorption capacity of soils demonstrated a reduction (p < 0.001) in comparison to the control sample (Figure 3). The magnitude of the decline in cation exchange capacity is contingent upon the concentration of oil products in the soil and the specific soil type. As illustrated in Figure 3, the greatest decrease in the cation exchange capacity was observed in podzolic soils, with a five-fold decline in this parameter at 100 or 150 g/kg of the oil products.

In the presence of oil products, the capacity of the soil to retain water is reduced (p = 0.005), the hydrosorption properties are impaired (Figure 4), and there is an increase in hydrophobic processes. Consequently, light fractions of oil, in small concentrations of approximately 50 g/kg, begin to affect the soil by penetrating its composition. The physical composition is the initial stage of the process, followed by changes in the chemical properties. The increase in oil concentration, achieved through uniform steps from 50 g/kg to 150 g/kg, has no further detrimental effect.

The preceding analysis demonstrates that the observed changes in the main physical and physicochemical properties are contingent upon the concentration of oil products in the soil. Specifically, the impact of oil is observed to diminish as the concentration of pollutants in the soil increases, and is most pronounced when the concentration of oil products reaches 50 g per kilogram of soil. Soils with a composition of light sandy and sandy loam are particularly susceptible to the effects of oil products.

3.2. Effects of the Surfactant on the Total Amount of Oil in the Contaminated Soil Samples

The degree of decomposition of the oil products was estimated in the presence of the non-ionic surfactant MS, which is used in oil production. The oil was incorporated into the soil in a ratio of 50 g/kg. The surfactant was utilized in a 1% concentration, with a 1:2 ratio (soil/surfactant). Figure 5 presents the findings of the research. As illustrated by the presented data, the presence of MS does not appear to affect the extent of compositional changes observed in the three oil-polluted soil types under investigation. It is noteworthy that, even after 35 days of treatment, the concentration of oil products in the soils did not undergo significant changes in the oil-polluted soils with the given surfactant. In the oil-contaminated sample without a surfactant, the natural decomposition of the oil products was estimated, with a range of 0.02 to 0.4%. The initial TPH contents in podzolic, sod-gley, and alluvial soils without oil contamination were 78 ± 31 mg/kg, 297 ± 51 mg/kg, and 341 ± 73 mg/kg, respectively.

4. Discussion

The present paper investigates the significant impact of oil contamination on the physical and chemical characteristics of various soil types located in taiga in Western Siberia, including podzolic, sod-gley and alluvial soils. The observed changes in pH levels, cation exchange capacity (CEC) and water retention ability demonstrate how oil products can affect soil health and functionality, with potentially severe consequences for soil productivity and environmental sustainability.

One of the most notable effects observed in the course of our study was the increase in pH levels of both water and salt extracts from the soils following the introduction of oil products (Figure 2). The observed increase in pH levels can be attributed to the alkaline nature of many oil products and their ability to neutralize acidic components within the soil [18]. This phenomenon has been observed in other studies, wherein oil contamination has been demonstrated to elevate soil pH, particularly in acidic soils such as podzolic soils. The observed pH rise is a cause for concern, given that soil pH plays a critical role in nutrient availability and microbial activity. A shift towards alkalinity could result in nutrient imbalances and a reduction in microbial diversity, which may ultimately lead to adverse effects on plant growth and soil fertility [18]. For example, Devatha et al. (2019) reported that crude oil raised soil pH in contaminated sandy soils, which disrupted nutrient availability and microbial diversity, thus complicating remediation efforts [36]. Moreover, the observation that pH changes reach a plateau at higher oil concentrations indicates that soils may possess a limited buffering capacity against the effects of oil contamination. This finding lends support to the conclusions of previous research, which indicate that soils may initially be capable of resisting changes in pH, but that this capacity may be lost once a certain contamination threshold is exceeded [37,38]. The observed increase in pH at 50 g/kg is of particular significance, as it suggests that even relatively low levels of oil contamination can result in significant soil degradation.

A further crucial consequence of oil contamination identified was the diminution of the cation exchange capacity (CEC) of soils (Figure 3). CEC is a measure of the soil’s capacity to retain and exchange essential nutrients, including calcium, magnesium and potassium [39]. The findings revealed a notable decline in CEC with elevated oil concentrations, particularly in podzolic soils, which demonstrated a five-fold reduction at oil concentrations of 100 and 150 g/kg. This reduction in CEC is a cause for concern, as it indicates that oil contamination can impair the soil’s ability to retain nutrients, which are vital for plant growth and ecosystem health. The reduction in CEC can be attributed to the hydrophobic nature of oil, which coats soil particles and thereby reduces their ability to interact with water and exchange nutrients [36,40]. This effect is particularly pronounced in soils with a lower organic matter content, such as podzolic soils, which are naturally less fertile and more susceptible to degradation. In contrast, sod-gley and alluvial soils, which have higher organic matter content, demonstrated less pronounced reductions in CEC, suggesting a certain degree of resilience to oil contamination. It has previously been reported that there is a decline in nutrient retention and exchange capacity following oil spills. For example, research conducted on sandy soils contaminated with oil revealed a comparable decline in CEC, which was attributed to the formation of oil films around soil particles. This emphasizes the long-term impact of oil contamination on soil fertility, as a reduction in nutrient retention can result in the leaching of nutrients, soil impoverishment and a decline in agricultural productivity. Furthermore, oil contamination was found to impair the water retention capacity of soils, with the most significant effects observed in the capillary moisture capacity of alluvial soils [41,42]. The findings demonstrated that oil contamination diminished the capacity of soils to retain water, with capillary moisture capacity declining from 34.29% to 28.1% in podzolic soils, from 29.7% to 26.4% in sod-gley soils, and from 24.5% to 21.4% in alluvial soils (Figure 4). The reduction in water retention capacity is accompanied by an increase in hydrophobic processes, which render the soils more resistant to water infiltration and retention. As demonstrated by Polyak et al. (2018), a comparable reduction in CEC has been observed as a consequence of the formation of oil films around soil particles. This has the effect of impairing the soil’s capacity to retain essential nutrients, such as calcium and magnesium. In sandy and loamy soils, a decline in CEC due to oil contamination is particularly deleterious, given that these soils already exhibit low natural fertility [43]. In such cases, effective remediation approaches may include the application of biochar or organic amendments, which have the potential to improve soil structure, enhance CEC, and promote microbial recovery. These methods have been demonstrated to be effective in the restoration of soil nutrient availability and overall fertility in oil-contaminated environments [3,4].

Soils with diminished water retention capacity are less capable of sustaining plant growth, particularly in arid and semi-arid regions where water availability is already constrained. The observed increase in hydrophobicity indicates that oil contamination not only impairs the soil’s capacity to retain water but also hinders the penetration of water into the soil. This can result in increased runoff, erosion and further degradation of soil structure [1,2,3,4]. Furthermore, a substantial body of evidence indicates that the hydrophobic character of oil products gives rise to the formation of water-repellent layers on the soil surface, which in turn reduces water infiltration and retention. This effect is particularly pronounced in light-textured soils, such as sandy loams, which are more susceptible to hydrophobicity [44,45,46]. The results of our study indicate that even relatively low concentrations of oil (50 g/kg) can have a considerable impact on soil hydrology, with the potential for significant implications for soil health and the provision of ecosystem services.

One of the principal findings of our study is the differential response of diverse soil types to oil contamination. While all three soil types (podzolic, sod-gley, and alluvial) exhibited some degree of degradation, the magnitude of the effects differed. Podzolic soils, which are distinguished by their acidic nature and low organic matter content, were the most severely affected, particularly in terms of changes in cation exchange capacity (CEC) and pH. In contrast, sod-gley soils, which have a higher clay and organic matter content, demonstrated a greater capacity to retain water and nutrients despite contamination by oil. Additionally, alluvial soils, which are typically more fertile, demonstrated a reduction in their capacity to retain water, yet exhibited less significant alterations in pH and CEC. The disparate impacts of oil contamination across soil types can be ascribed to variations in soil structure, texture and organic matter content. Soils with a higher organic matter content and clay particles are better able to buffer against the effects of oil contamination, as they can retain more water and nutrients. In contrast, soils with low organic matter content, such as podzolic soils, are more susceptible to degradation, as they have a limited capacity to retain nutrients and resist changes in pH. It has been documented that there are differential responses of soil types to oil contamination. For example, studies conducted on clay-rich soils have demonstrated that these soils exhibit greater resistance to degradation due to their elevated CEC and water retention capacity. Conversely, sandy soils, which exhibit a lower organic matter content and CEC, demonstrate greater susceptibility to the effects of oil contamination, particularly in regard to hydrophobicity and nutrient leaching [47,48].

A further objective of this study was to ascertain whether the incorporation of MS surfactant, without any supplementary intervention, could facilitate the decomposition of oil-derived substances in the contaminated soil samples. MS is a commonly used chemical in oil production, and previous studies have demonstrated that it increases the mobility and bioavailability of oil pollutants in other contexts [49]. However, the study results indicated that the surfactant had a negligible effect on the total quantity of oil present in the soil samples, even after a treatment period of 35 days. The study revealed that in the absence of the surfactant, the natural decomposition of oil in contaminated soils occurred at a markedly slow rate. The total petroleum hydrocarbon (TPH) content in podzolic, sod-gley, and alluvial soils without oil contamination was found to be 78 ± 31 mg/kg, 297 ± 51 mg/kg, and 341 ± 73 mg/kg, respectively (Figure 5). This demonstrates the intrinsic capacity of these soils to accommodate a certain level of contamination, although the natural decomposition of oil products was minimal (ranging between 0.02% and 0.4%). Given the inherent resistance of petroleum hydrocarbons to biodegradation, as a result of their complex molecular structure, it is unsurprising that the soils displayed a limited capacity for natural decomposition. Furthermore, the resilience of oil contaminants indicates that natural remediation, even over extended periods, is an inadequate method for significantly reducing oil concentrations, particularly when faced with high levels of contamination. This finding is consistent with the results of other studies in the literature, which have documented the slow natural attenuation of hydrocarbons in contaminated soils under non-optimized conditions [50,51]. The findings indicate that remediation strategies should be tailored to specific soil types. In conclusion, further research is required to identify the conditions under which surfactants used in the oil industry can be beneficial, both for enhancing the efficacy of oil production and for initial contaminated coil treatment. This is while the scientific community continues to search for optimal conditions for achieving meaningful reductions in oil contamination. Additionally, Wei et al. (2020) reported that oil contamination reduced water infiltration and retention in sandy loam soils. The observed hydrophobicity, which results in increased runoff and erosion, indicates that surfactant application may not be an adequate solution for heavily contaminated soils. Alternatively, techniques such as biostimulation with hydrocarbon-degrading microbes, in conjunction with soil amendments to enhance porosity, may prove more efficacious in reversing hydrophobicity and restoring water retention [43].

In conclusion, these findings emphasize the importance of developing remediation strategies that are tailored to the specific characteristics of the soil and the levels of contamination present. Techniques such as pH stabilization, the use of organic amendments to enhance cation exchange capacity (CEC), and combined surfactant–microbe applications represent promising approaches to the management of the complex challenges posed by oil-contaminated soils in diverse taiga ecosystems. Such bespoke strategies not only enhance the efficacy of remediation processes but also align with the principles of sustainable soil management, thereby promoting the long-term health of the soil and resilience of the ecosystem.

5. Conclusions

This study demonstrates the profound impact of oil contamination on the key physical and chemical parameters of soils in the middle taiga region of Western Siberia, affecting podzolic, sod-gley, and alluvial soil types. The contamination of soil with oil leads to substantial shifts in the pH, cation exchange capacity (CEC), and water retention capabilities of the soil, each of which is crucial for the sustainability of soil fertility and ecological stability. Podzolic soils, due to their lower organic content and higher acidity, exhibit the most pronounced degradation, while sod-gley and alluvial soils show greater resilience, yet still experience significant functional impairments.

It is of the utmost importance to comprehend these alterations to the parameters in order to select the most efficacious remediation technologies for contaminated soils. By identifying the manner in which different soil types respond to oil contamination, remediation strategies can be developed on a case-by-case basis, with the aim of optimizing recovery efforts according to the specific needs of each soil type. This approach not only enhances the effectiveness of remediation, but also ensures the sustainable management of soil health in these sensitive ecosystems.

Furthermore, the findings of this study provide a foundation for the development of specialized software for the analysis of soil pollution. The data presented in Figure 2, Figure 3, Figure 4 and Figure 5 could be used to construct mathematical models for calculating and predicting changes in soil properties due to oil contamination. The integration of such models into analytical software would facilitate the real-time assessment and forecasting of soil pollution impacts, thereby supporting informed decision-making in the context of pollution management and remediation planning. These tools could prove invaluable to environmental professionals engaged in the design of adaptive, data-driven responses to soil contamination challenges across a range of taiga ecosystems.